Dirty Pretty Things (15)

The last time director Stephen Frears splashed down on immigrant London was back in the Eighties when the inter-racial romance of My Beautiful Launderette put grey old Thatcherite Britain through the mangle. Having sifted gold (The Grifters) and guff (Hero, Mary Reilly) in the canyons of Hollywood since then, Frears has returned to these shores in Dirty Pretty Things to present an unsettling portrait of the capital: here is a London without landmarks and, for the most part, without Londoners. True, the film guides us through traffic jams (it's not that unrecognisable) and street bustle, but there's a conscious evasion of specific neighbourhoods: this is a place of anony-mity, where an invisible army of low-paid immigrant workers keeps things running.

One such is Okwe (Chiwetel Ejiofor), a Nigerian refugee who works as a minicab driver by day and a hotel concierge by night. The few hours left to him he spends not being able to sleep and playing chess with his friend Guo Yi (Benedict Wong), a dryly philosophical mortuary attendant.

"This is a weird city," observes the latter, and just how weird Okwe is about to find out. Called to unblock an overflowing toilet in one of the hotel rooms, he extracts from the S-bend a grey lump of muscle, which, as a one-time doctor, he knows to be a human heart. They said nothing about this in the job description. Okwe reports this unlovely find to the chief concierge, the Dickensianly named Sneaky (Sergi Lopez) and demands that the authorities be alerted. But Sneaky is true to his name, and makes sure that Okwe, an illegal alien, doesn't go blabbing to the police. The trafficking in human organs is apparently a lucrative business.

Okwe rents sofa space in the tiny bedsit of Senay (Audrey Tautou), a beautiful Turkish immigrant also struggling to make ends meet. Like him, she shuttles between two jobs, a chambermaid at the hotel and seamstress in a sweatshop where the boss has her on her knees in return for keeping immigration officials off her back. This is lowdown, dirty work for an actress who made her name on the cloying sweetness of Amélie, and I wondered if Tautou could handle such a drastic switch, from paragon of homeliness to put-upon exile. She can, and does. The innocence is still there in those treacle-dark eyes but now there's wariness too, and her quick, nervous steps betoken a soul who fears violation at any minute – as well she might. Only in Okwe's company does Senay let her guard down, and Chiwetel Ejiofor's heroically understated playing tells us why; in Okwe he locates goodness without piety, and nobility without arrogance. I've seen few performances that convey quiet self-effacement so powerfully.

The idea of everyday invisibility was also at the core of Ken Loach's film Bread and Roses, which examined the plight of Los Angeles's immigrant cleaning workers, similarly trapped between the exploitation of employers and the hounding of immigration control. But where Loach was prone to fist-shaking didacticism, Frears and his writer Steven Knight equip the story with a thriller's urgency.

Knight is also co-creator of the quiz show Who Wants To Be A Millionaire, not the most obvious grounding for a screenwriter, one might think, though it has probably helped him understand the psychology of competition and survival. (Here the show's title would be Who Wants To Be A British Passport Holder?, the document that asylum seekers are willing to trade their internal organs for.) Some elements work better than others. I'm not convinced by the Gothic detail of the ticker-in-the-toilet: selling your kidney is plausible, but selling your heart is surely impossible for anyone bar a divorce lawyer. And I don't think somebody as cunning as Sneaky would fall for the old spiked-drink trick, especially at such a vital juncture in the plot.

On the other hand, Ejiofor and Tautou become very affecting as they look for ways to protect each other from the immigration snoops. "Stick to helping people who can be helped," Okwe is told, but he's a man who can't help himself helping out the helpless, even though dark rumours circulate about what happened to his wife back in Lagos.

While Dirty Pretty Things sounds hellishly bleak, and cinematographer Chris Menges pokes around the murkiest corridors and backstairs, the ominous atmosphere feels leavened by a wry, hangman's humour. This is due in part to Zlatko Buric as the hotel's randy doorman, Sophie Okonedo as the tart-with-a-heart (incidentally, when did you last see a movie in which the tart was without a heart?) and to the tatty circumstances in which Okwe's professional expertise is called upon.

As all doctors will know, it's an occupational hazard that the most casual acquaintances feel entitled to consult them on their latest aches and pains, but I imagine very few have had to do a backroom diagnosis on a trio of minicab drivers stricken with the clap.

With asylum seekers in the headlines at the moment the film could hardly be more timely, and its picture of a whole service industry hiding in plain sight will give anyone with a conscience something to ponder. As for Frears, it marks an upward curve on his uneven career path; not always able to pick the right projects, he is here very close to the top of his game, drawing an unusual portrait of London, that "weird city", and from Chiwetel Ejiofor a performance to rank among the very best of the year.